earth covered by water originally

Regarding the question you have asked, you can give a very straight answer. Bhagavad-gita says, "dehantara praptih [Bg 2.13]''. The soul transmigrates, but there is no regular process. In the beginning of creation, when all the world was water, all living entities were aquatics. Then gradually from aquatics the soul passes into plant bodies, then insect bodies, then bird bodies, then animal bodies, then human beings. In the human form the soul can decide whether to go back to home, back to Godhead or return to birth and death, accepting material bodies according to his karma. Therefore, it is advised to take advantage of the human form of body to go back home, back to Godhead. Our movement is for this purpose, to offer all human beings a chance to go back home, back to Godhead.    (More...)